FIG. 16 is a block diagram showing a conventional programmable controller disclosed in Japanese patent application laid open No. 07-334211. As shown in this figure, the programmable controller 10 comprises a processor 11 and memory 13, and is connected to a monitoring device 20. The monitoring device 20 is used for setting data required by the programmable controller 10 and also displaying the data. The processor 11 is connected to the memory 13. The processor 11 has a debugging interruption function like Intel-produced 80486, and also has a built-in debugging register 19. The debugging register 19 can generate debugging interruption, if an arbitrary address of data is set, immediately after the address is accessed. The memory 13 stores program in a program area 14, variables in a variable area 15, and trace data in a trace area 17.
The operation of the controller is explained below with reference to FIG. 17. FIG. 17 shows a frame example of the monitoring device 20. Reference numeral PN1 to PN4 represent program numbers, PS1 to PS4 represent step numbers, and D1 to D4 represent values of a variable. FIG. 17 shows the case where four types of trace data (which are indicated by trance numbers 1 to 4) are included in one variable name A. The user of the programmable controller sets a variable name while viewing the screen of the monitoring device 20. The set variable is converted into an absolute address that is processor 11-recognizable by the operating system, and set in the debugging register 19. The program are repeatedly executed by the operating system at constantly cycled time intervals. When the access is made to the address set in the debugging register 19 during execution of the program, the processor 11 generates debugging interruption. The operating system reads out the program number (PN1 to PN4) of the program that is currently operating, the program step number (PS1 to PS4), and the values (D1 to D4) of the accessed variable within the debugging interrupt handler, and stores the read-out data in the trace buffer 17. The monitoring device 20 reads out the data in the trace area 17 of the memory 13, and displays the data on the screen of the monitoring device 20.
Even if the programmable controller technology disclosed in the Japanese patent application laid open No. 07-334211 is employed for a robot controller having a large number of variables as explained above, it is required to repeat debugging a plurality of times according to the variables if there are many specific variables that have trouble. Therefore, a lot of time is required for trouble shooting.
Like the program debugging method disclosed in Japanese patent application laid open No. 04-332052, there is another technology that compiles a source program to create a load module file and pursuit information file and specifies a plurality of variables to be displayed. According to this method, however, various types of file and table are created once. Therefore, there is a problem that a large memory capacity is required.